Heretofore backlash was reduced in tuning machines by forcing the worm laterally into full mesh engagement with the worm gear. U.S. Pat. No. 3,564,573 issued on Feb. 16, 1971 to Wustl, shows a worm spring urging the worm screw tightly against the worm gear. End play was reduced by trapping the worm axially between two stop structures.
Heretofore end play was reduced in tuning machines by forcing the worm axially against a stop to prevent axial displacement during operation. U.S. Pat. No. 4,098,163 issued on July 4, 1978 to Kato, shows an adjustable axial sleeve mounted around the worm shaft. The sleeve is threaded and is positioned to pin the worm shaft against the housing. Axial movement (end play) is prevented by the housing at one end of the worm shaft and by the sleeve at the other end. These prior art devices do not permit the simultaneous reduction of both backlash and end play with a single adjustment.